The demands on automobiles for better fuel economy have been increasing in recent years as concern with environmental issues has been rising. Good fuel economy is also being required of the rubber compositions used for automotive tires.
Patent Literature 1, for example, proposes a method for enhancing the fuel economy. This method uses a diene rubber that has been modified with an organosilicon compound containing an amino group and an alkoxy group. These days, however, further enhancement of the fuel economy has been demanded. Meanwhile, wet-grip performance and abrasion resistance are also properties required of the rubber compositions for automotive tires; however, these properties generally assume an inverse relationship with the fuel economy. Thus, it has been difficult to achieve these properties at high levels in a balanced manner.
Moreover, polybutadiene rubber is generally used to enhance abrasion resistance. The use of butadiene rubber having a higher molecular weight enhances abrasion resistance; however, it unfortunately reduces kneading processability. Thus, a method has been demanded that can enhance fuel economy, wet-grip performance, abrasion resistance, and kneading processability in a balanced manner.